How do I use glycerin to avoid fondant from drying out?

If you are making your own fondant then you would add the amount listed in the recipe. If using ready made fondant you can lightly coat your hands (I emphasize lightly)  with a little shortening, just roll and stretch the fondant a little.  This puts the shortening on and into the fondant making it smoother.  Be sure to roll leftover fondant or 50/50 into a log and coat with shortening, roll with a couple layers of plastic wrap and store in a zip lock bag, squishing the air out.  Hopefully this is what you wanted to know. 

Thank you. I was watching a cake challenge show and the bakers fondant was very dry and tore when she placed on cake and they mentioned it looked like "elephant skin".  They said she should add more glycerin to fondant; I thought it was ready made fondant, but maybe not.

You can use glycerin and it does the same thing however, my personal is using a little shortening. When I use fondant, 50/50 or gum paste I have a small plastic container filled with shortening near me. I use this so as I am dipping fingertips into it I will not contaminate the large container I use for baking. Use what you prefer, no rule that you have to use a particular one.  No on will knock on your door to check what you are using.

AHi, I use Bakels Pettinice for covering cakes and just personally I have found the glycerin to be better than shortening, just adding a little at a time.